1. Field of the Invention
The present invention relates to a light quantity control apparatus used in various camera devices such as video cameras and still cameras. Specifically, it relates to a light quantity control unit such as a diaphragm for regulating the amount of light in a photographing operation or a shutter for blocking the light in a photographing operation.
2. Description of the Related Arts
This type of light quantity control unit is comprised of a ring shape base plate integrated in the photographing lens part and has an aperture, one or a plurality of blade members being revolvingly mounted to this base plate and border on the aperture, and an electro-magnetic drive unit interlocked to the blade member and mounted to said base plate. By applying an electric current to this electro-magnetic drive unit, said blade member revolves and the aperture is blocked or the diameter of the aperture is reduced.
Conventionally, this electro-magnetic drive unit was integrated into one unit with said base plate and various methods thereof have been proposed. As a representative drive unit, there is a method of supporting and holding a magnetic rotor with a coil frame revolving freely, winding a coil on the coil frame to envelope the rotor, covering the periphery thereof with a yoke, and revolving the rotor according to Fleming""s left-hand rule by exciting this coil as is disclosed, for example, in Japanese Patent Publication (Kokaihei) No. 10-221740. As described in Kokaihei 10-221740, it is proposed that this drive unit is mounted on the aforementioned base plate to transmit the rotating force of said magnet rotor to the blade member.
Also, there is another method of supporting and holding a magnet rotor at the peripheral part of the base plate in the direction of the optical axis, mounting a coil wound similarly at the peripheral part in the direction orthogonal to the optical axis, opposingly arranging the leading ends of a pair of soft magnetic members, each end being connected to said coil at the periphery of said magnet rotor, forming magnetic poles at the leading ends of these soft magnetic members by conducting to the coil, and obtaining a turning torque between the magnetic poles polarized in the magnetic rotor as is proposed, for example, in Japanese Patent Publication (Kokaihei) No. 6-258683. When using this method, a coil, paired soft magnetic members and a magnetic roller are arranged.
To reciprocally operate blade members in the opening and closing directions with a prescribed angle in the conventional drive apparatuses, an operation regulating means such as a stopper, for example, was established between the drive unit and the blade members.
In the conventional regulating means, the notable force of the rotational torque is applied when rotating blade members from a closed state to the opening direction, and conversely, the rotational torque is applied when rotating blade members from an open state to the closing direction. It is obvious that the operation to open and then to close these blades is symmetrical and that it is necessary to control the photographing conditions.
However, in recent cameras that are equipped with photoelectric converting elements, there are cases in which the closing operation from the blade members being in an open state is used in a photographic condition such that the camera leaves the shutter blades open when not operating and closes them when photographing an image. Because quick-operation is required in the closing direction for the blade members at such time, the supplied current of the drive device is large and there must be many coils of wire, so the problem of the large consumption of power supplied and the enlarging of the device occur.
An object of the present invention is to provide a light quantity control apparatus enabling speed control of photographic light quantity control such as the shutter blades according to the camera device photographic conditions without enlargement of the device nor large electrical power consumption, and to provide a camera device incorporating these light quantity control devices.
In order to achieve the aforementioned purpose, this invention is composed as follows.
First of all, a blade member having an optical axis aperture is arranged on a base plate to a border on the aperture. The apparatus includes a freely rotating magnet rotor linked to the opening and closing of the aforementioned blade members, a coil applying rotational torque to the magnet rotor and/or a soft magnetic member. Also, the rotational torque that acts on the aforementioned magnet rotor is made to be different from the regulating means that regulates the movement in the opening region and closing region of the shutter blades between the opening region and closing region of the shutter blades. What is further desirable is to attain this by establishing regulating means in positions where, in the opening and closing regions, the distance of the gap differs between the magnetic poles mounted to the aforementioned magnet rotor and the soft magnetic members that applies rotational torque by attracting with the magnetic poles. Also, this can be achieved by differing the revolving force of the coil that applies revolving torque to the aforementioned magnet rotor, in the aforementioned opening region and the closing region.
The aforementioned blade member can be a shutter blade to block the aforementioned optical axis aperture or it can be a diaphragm to regulate the amount of light from the optical axis aperture.
Particularly, in this invention, paired soft magnetic materials that abut the base end parts on the aforementioned coil and the aforementioned magnet rotor are arranged to the aforementioned base plate, the leading end of these paired soft magnetic materials are opposingly established to sandwich the aforementioned magnet rotor. A magnetic field is generated by the energized state of the aforementioned coil and is lead to the aforementioned soft magnetic materials thereby the aforementioned soft magnetic materials attract the magnetic poles mounted on the aforementioned magnet rotor. When the aforementioned coils are in a non-energized state, the magnetic poles mounted to the aforementioned magnet rotor are attracted by the aforementioned soft magnetic material causing rotational torque on each of the aforementioned magnet rotors which can be applied to the light quantity control apparatus.
Such a structure enables the quick opening and quick closing operations that match the photographic conditions of the camera on which it is used without an increase in the consumption of power or the number of coils.